Optical isomerism
Introduced| English | Meaning |
|---|---|
| enantiomer/eˈnæntɪəmə/ | enantiomer |
| plane-polarised light/pleɪn ˈpəʊləraɪzd laɪt/ | plane-polarised light |
| optically active/ˈɒptɪkli ˈæktɪv/ | Able to rotate the plane of plane-polarised light; a property of chiral compounds. |
| racemic mixture/rəˈsiːmɪk ˈmɪkstʃə/ | A 50:50 mix; it gives no net rotation (the two opposite rotations cancel). |
| chiral centre/ˈkaɪrəl ˈsentə/ | An atom, commonly carbon bonded to four different groups, around which arrangements can produce non-superimposable mirror images. |
Left hand, right hand
- Two enantiomers 对映体 are mirror-image isomers.
- They are identical in almost every property — with two exceptions.
- This matters greatly for medicines.
Optical isomerism lab
Identify when a molecule can have non-superimposable mirror images.
A carbon atom bonded to four different groups is a ______ (asymmetric) carbon.
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It gives rise to optical isomers.
Enantiomers and optical activity
- Enantiomers have identical physical and chemical properties, except:
- they rotate plane-polarised light 平面偏振光 in opposite directions (they are optically active 旋光活性).
- they may have different biological effects.
- A racemic mixture 外消旋混合物 is a 50:50 mix; it gives no net rotation (the two opposite rotations cancel).
Enantiomers rotate plane-polarised light in opposite directions
Two enantiomers differ in that they:
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Enantiomers are otherwise identical; they rotate plane-polarised light oppositely and can act differently in the body.
A racemic mixture (50:50 enantiomers):
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The equal, opposite rotations of the two enantiomers cancel out.
A single pure enantiomer is optically active (it rotates plane-polarised light).
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A pure enantiomer rotates the plane of polarised light; only a racemic mixture cancels out.
Chirality and drugs
- A molecule with a chiral centre 手性中心 has two enantiomers — and they can behave very differently in the body (one may cure, the other harm).
- So drug makers either separate the racemic mixture into pure enantiomers, or use a chiral catalyst to make just the one they want.
Why does chirality matter when making drugs?
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One enantiomer may cure while the other harms, so makers separate them or use a chiral catalyst.
Recognising optical isomers
- Optical isomers are non-superimposable mirror images (enantiomers).
- They rotate plane-polarised light in opposite directions.
You've got it
- enantiomers are mirror images: identical properties except they rotate plane-polarised light oppositely and may differ in biological effect
- a racemic mixture (50:50) gives no net rotation
- chirality matters for drugs — separate the enantiomers or use a chiral catalyst